Metrology system for measuring edge of circular workpiece

Abstract

A metrology system includes an illumination configuration having an illumination source, an objective lens configuration, and an image sensor configuration including an image sensor. The objective lens configuration includes an objective lens and has a lens optical axis. The illumination configuration, the objective lens configuration and the image sensor configuration form an optical path along which illumination from the illumination configuration travels. The illumination configuration provides illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along the optical path. At least part of the illumination configuration is tilted relative to the objective lens configuration such that the illumination direction is at a first tilt angle in relation to the lens optical axis. The objective lens configuration directs illumination toward the image sensor configuration which is configured to provide an image corresponding to the edge of the circular workpiece.

The invention claimed is: 
     
       1. A metrology system, comprising:
 an illumination configuration comprising an illumination source; 
 an objective lens configuration comprising an objective lens and having a lens optical axis; and 
 an image sensor configuration comprising an image sensor; 
 wherein:
 the illumination configuration, the objective lens configuration and the image sensor configuration form an optical path along which illumination from the illumination configuration travels; 
 the illumination configuration is configured to provide illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along the optical path; 
 at least part of the illumination configuration is tilted relative to the objective lens configuration such that the illumination direction is at a first tilt angle in relation to the lens optical axis of the objective lens configuration; 
 the circular workpiece comprises the edge and first and second planar surfaces, for which a first tilt direction corresponding to the first tilt angle is nominally parallel to the first and second planar surfaces; and 
 the objective lens configuration directs illumination toward the image sensor configuration which is configured to provide an image corresponding to the edge of the circular workpiece. 
 
 
     
     
       2. The system of  claim 1 , wherein the first tilt direction and the first tilt angle lie in a first tilt angle plane that is parallel to the first and second planar surfaces. 
     
     
       3. The system of  claim 1 , wherein the illumination direction is nominally parallel to the first and second planar surfaces. 
     
     
       4. The system of  claim 3 , wherein at least part of the illumination configuration is configured to be adjusted to adjust the illumination direction to be nominally parallel to the first and second planar surfaces. 
     
     
       5. The system of  claim 1 , wherein the first tilt angle is at least one degree. 
     
     
       6. The system of  claim 1 , wherein the first tilt angle is at least two degrees. 
     
     
       7. The system of  claim 1 , further comprising a rotation mechanism configured to rotate the circular workpiece. 
     
     
       8. The system of  claim 1 , wherein the illumination configuration further comprises an illumination source aperture that is not circular. 
     
     
       9. The system of  claim 1 , wherein the illumination source is not a white illumination source and provides only a single color of illumination. 
     
     
       10. The system of  claim 1 , wherein the image sensor is tilted relative to the objective lens configuration such that a sensor direction is at a sensor tilt angle in relation to the lens optical axis of the objective lens configuration. 
     
     
       11. The system of  claim 1 , wherein the objective lens configuration further comprises an aperture component with an aperture that is asymmetric about the lens optical axis and that is configured to block low angle scattered illumination. 
     
     
       12. The system of  claim 1 , wherein the image corresponding to the edge of the circular workpiece is a shadow image which comprises a shadow of the edge of the circular workpiece. 
     
     
       13. A method for operating a metrology system,
 the metrology system comprising:
 an illumination configuration comprising an illumination source; 
 an objective lens configuration comprising an objective lens and having a lens optical axis; and 
 an image sensor configuration comprising an image sensor; 
 
 the method comprising:
 operating the illumination configuration to provide illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along an optical path, wherein:
 at least part of the illumination configuration is tilted relative to the objective lens configuration such that the illumination direction is at a first tilt angle in relation to the lens optical axis of the objective lens configuration; 
 the circular workpiece comprises the edge and first and second planar surfaces, for which a first tilt direction corresponding to the first tilt angle is nominally parallel to the first and second planar surfaces; and 
 the objective lens configuration directs illumination toward the image sensor configuration; and 
 
 operating the image sensor configuration to provide an image corresponding to the edge of the circular workpiece. 
 
 
     
     
       14. The method of  claim 13 , further comprising utilizing the image for performing a measurement process for determining a measurement of the edge. 
     
     
       15. The method of  claim 14 , wherein the measurement process comprises determining coordinates of a point on the edge. 
     
     
       16. The method of  claim 14 , wherein the measurement of the edge has a higher accuracy due at least in part to the first tilt angle, in comparison to a measurement that would result from a similar configuration without the first tilt angle in which the illumination direction was correspondingly coaxial or parallel with the lens optical axis. 
     
     
       17. The method of  claim 13 , further comprising adjusting at least part of the illumination configuration to adjust the illumination direction to be nominally parallel to first and second planar surfaces of the circular workpiece. 
     
     
       18. An illumination configuration for use in a metrology system,
 the metrology system comprising:
 an objective lens configuration comprising an objective lens and having a lens optical axis; and 
 an image sensor configuration comprising an image sensor; 
 
 the illumination configuration comprising an illumination source; 
 wherein:
 the illumination configuration, the objective lens configuration and the image sensor configuration form an optical path along which illumination from the illumination configuration travels; 
 the illumination configuration is configured to provide illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along the optical path; 
 at least part of the illumination configuration is tilted relative to the objective lens configuration such that the illumination direction is at a first tilt angle in relation to the lens optical axis of the objective lens configuration; 
 the circular workpiece comprises the edge and first and second planar surfaces, for which a first tilt direction corresponding to the first tilt angle is nominally parallel to the first and second planar surfaces; and 
 the objective lens configuration directs illumination toward the image sensor configuration which is configured to provide an image corresponding to the edge of the circular workpiece. 
 
 
     
     
       19. The illumination configuration of  claim 18 , wherein at least part of the illumination configuration is configured to be adjusted to adjust the illumination direction to be nominally parallel to the first and second planar surfaces. 
     
     
       20. The illumination configuration of  claim 18 , wherein the image corresponding to the edge of the circular workpiece is a shadow image which comprises a shadow of the edge of the circular workpiece.